Downhole oil and gas tools are often subject to harsh, corrosive or otherwise extreme downhole environments. Accordingly, metal pre-treatments, final treatments, finishings and coatings may be applied on downhole tool surfaces as protection. In one aspect, embodiments disclosed herein relate to a downhole tools such as mandrels including a circumferential band comprising a plurality of axially adjacent weld beads forming a wear resistant surface along a particular axial length of the mandrel and at least one circumferential multi-layer coating applied axially adjacent the band on either end, the coating including a first layer, exhibiting a first color, applied directly onto the mandrel surface, and a second wear-resistant layer, exhibiting a second color different from the first color, applied directly onto the first layer, wherein when the second layer wears or is removed by a certain amount, the first color of the first layer is revealed to indicate the mandrel should be removed from service and a new wear-resistant coating reapplied.
In another embodiment a downhole tool is disclosed comprising a circumferential band comprising a plurality of axially adjacent weld beads forming a wear resistant surface along a particular axial length of the tool. The tool may have at least one circumferential multi-layer coating applied axially adjacent the band on either end. The coating comprises a first wear-resistant layer, applied directly onto the tool surface; a first color layer, exhibiting a first color, applied to said first wear-resistant layer; a second wear-resistant layer, exhibiting a second color different from the first color, applied directly onto the first color layer. When the second wear-resistant layer wears or is removed by a certain amount, the first color of the first color layer is revealed as an indication of the degree of wear.
In other aspects, embodiments disclosed herein relate to a method of applying a multi-layer coating axially adjacent at least one end of a circumferential wear band located along a particular axial length of a downhole tool, the wear band comprising a plurality of axially adjacent weld beads, the method including applying a first layer, the first layer exhibiting a first color, directly onto a surface of the downhole tool surface axially adjacent to the wear band and applying a second wear-resistant layer, the second layer exhibiting a second color different from the first color, directly onto the first layer and substantially axially adjacent to the wear band, wherein when the second layer wears or is removed by a certain amount, the first color of the first layer is revealed to indicate the downhole tool should be removed from service and a new wear-resistant coating reapplied.